Data dictionary tables are not directly accessible, but you can access information in
them through data dictionary views. To list the data dictionary views available to
you, query the view DICTIONARY. Many data dictionary tables have three corresponding views:

An ALL_ view displays all the information accessible to the current user,
including information from the current user's schema as well as information
from objects in other schemas, if the current user has access to those objects by
way of grants of privileges or roles.

A DBA_ view displays all relevant information in the entire database. DBA_
views are intended only for administrators. They can be accessed only by users
with the SELECT ANY TABLE privilege. This privilege is assigned to the DBA
role when the system is initially installed.

A USER_ view displays all the information from the schema of the current user.
No special privileges are required to query these views.